I have a 1960's Michigan 175-A with a two pedal air brake with declutch system. I spent some time getting the brakes cleaned up and have them adjusted to where the shoes barely touch the drum by eye. I can get it to stop fairly well with the declutch side pedal( although sometimes I have to get down and get the declutch valve unstuck) But it does not have much braking with the non declutch pedal. yes the system is quite old so there are tolerance issues and prob not as much pressure as there used to be but Im wondering where to start looking to improve it a bit. Im wondering If I should just add more pressure on the shoes or if I need to start looking more closely at the air pressure or if its a physical problem with the pedal air plunger. anyone who has worked with this system before has any knowlege to share id be greatful many thanks in advance Tarik
Can you post a pic of the shoes and adjuster? is it an S-cam system?
Yes Thanks. mom not sure what the style is called
I could come up with all kinds of things to check but maybe one of the best might be to get some pipe fittings and at the air line connection on one of the brake chambers install a Tee in the system so you can see the air pressure that is going to the brake chamber when each foot brake is being applied. Compare this to the air pressure at the air tank. Basically with a good hard application of either brake peddle you should see the same or very close pressure as you have in the air tank. If not you might have a problem in the brake valve either internal restriction or leaking or the pivot for the peddle could be restricting its movement. Might want to do this test with engine off so you can hear leakage if there is any. Best would be if you have a shop compressor that you could connect to the tank to keep air pressure more or less constant while testing. Other than a drop in tank pressure when brakes are first applied you should be able to hole the brake on steady with no further loss of air pressure. If how ever the pressure continues to drop you have a leakage problem that you need to find!
Ok Thanks Kshansen What kind of pressure should I be getting?
Well if you have full air pressure in the air tank of say 120 PSI with a good hard push on either brake peddle that is what you should see at the brake can.
ok what kind of pressure are these compressors supposed to make and keep? what is the minimum acceptable pressure to run those air brakes ? as I imaging the compressor may be worn
Just like any air brake system. Air governor should turn on (cut in) the compressor at 95 psi and then cut out the compressor at 120 psi.
All good info you gave KS, but the applied air to stop would be around 30 psi or less depending on foot valve and type of relay valve. The foot valve is control pressure which signals relay valve that is fed direct air from tank. Relay will open at a predetermined cracking pressure allowing air from tank to brake air chamber. For instance normal brake application on a semi for a standard controlled stop is around 20 to 25 psi, applied air for an emergency stop would be in the area of 60 to 65 psi-that's at the air chambers. Like KS said tee the line at air brake chamber to check applied air at air chambers. The areas to check if low psi-first check the relay valve-Probably at that vintage a R-6 valve {just guessing}. Those brake shoes will be hard to find possibly-being bolt type cast web. S-Cam. One other thing is type of air chamber and size-possibly a #24's.
Thanks for the Info TS, ill get on it and report back. so Tee on the line side of the air chambers and find pressure there and tank pressure. got it. but if the air leak is happening in the chambers how do I determine that? Is it just one big replacable diphram for each chamber or do you replace the chamber...
Before you test the air system, snug the adjuster down, then back off a quarter turn, test drive it. That's how you adjust S-cam brakes.
Maybe I'm missing it but looking at that plumbing diagram in post #10 I'm not seeing any relay valves. Now I'm trying to recall if the old Michigans I worked on had relay valve or if the air went straight from the E-2 brake valves. I may be off but seems some only have a quick release valve in the lines.
Did some investigating on Bendix and find this for the E-2 and E-3 brake valves. I may not have worded it right but this is what I was trying to say. SERVICE TESTS Operating Test (IMPORTANT!!! Tests should be conducted with an accurate test gauge.) Install gauge in a delivery port or line; depress the treadle or pedal to several positions between fully released and fully applied positions, checking the delivery pressure on the gauge to see that it varies proportionately with the movement of the treadle or pedal. In the fully applied position, the reading on the gauge should be approximately that of full reservoir pressure. Upon release of the application, the reading of the test gauge should fall to zero psi immediately
Ok will do Thx
Thanks for looking into it for me. I’ll report back
Interesting. That is a lot of applied pressure. Was that a general Bendix form or one related to Clark? Because if that was a general form it is incorrect.
Pls forgive my ignorance But I’m a bit lost What bendix are you referring to? Is it possible to explain it to me ? Or is it too much to write
Well above KS refers to Bendix E2 & E3 foot treadle valve test-which is a single circuit foot valve. No big deal there and the Michigan diagram does not show a relay valve. What I find interesting is relay valves are commonly used in a air brake system, mainly for greater/faster/smoother control. Running a air brake system off just a foot valve is really strange, even though it's just a loader not a truck brake system. The Bendix test is flawed for the reason a relay is always used. The relay stops the flutter from foot action at the pedal. A 60 plus psi application without ABS will lock up the brakes. A 70 psi application is the same as a park brake chamber set. So Bendix saying a test should show 120 max applied is rather oddddd. It only takes 70 psi to release a park brake chamber.
Another-it's why there are different diameters of brake chambers-it works on volume rather than high psi. Although it's probably one of those things where a loader with low speeds doesn't require a relay. But KS has worked on these I haven't/not questioning his authority more like the Bendix info, because I have found mistakes before with Bendix listings for air valve applications.
ok. Thanks for the all the info and clarification and the nods to KS That’s what makes all the good stuff happen in the world. I am forever grateful when people take time to help me learn …..I must love learning /working on all these old machines cause I can’t seem to stop Ha ha !
I'll see if this will attach:
I could not find any online manuals for the old Michigans but just for kick I spent some time looking at parts break downs on Cat 966C loaders. Maybe a little bigger machine but about the same vintage as the 175. Other than a double check valve to segregate the right and left foot brake valves the only other valves in the system are two quick release valves. One for each axle, front and rear. With apologies to the original poster for hi-jacking his thread: I did also check the brake systems on a 980 Cat and sure enough that machine used relay valves front and back. But one thing that someone not familiar with front end Cat loaders would be the fact that the front axle of that machine has two Maxi-brake chambers on each brake camshaft! Also if you look close you might notice that the rear brake chambers are a larger size than the ones used on the front!
And that test statement has been incorrect since it was printed years ago. Since relay valves have a average cracking psi of 5 psi and the application gage shows 20 psi it will have 20 psi at air chamber for normal braking. At 70 psi the brakes are in a full lock up. During a DOT inspection most inspectors will tell the driver to apply full app of no less than 60 psi when they are checking brake function.
Thanks for posting that KS.
Well at least we are not having to deal with air over hydraulic wedge brakes on this loader! Or bladder brakes with hydraulic accumulators like a 988 87A Cat!
Guess while adding to this thread and probably confusing the original poster I should have included a drawing of the 966C brake system that shows no relays: Those two lines in the upper right corner are the out let from air compressor and the line from reservoir to the air governor. Again Tarmop, sorry about getting off on a bit of a tangent in your thread. Hope you can get this Michigan stopping right. I did not have a bunch of experience on Michigan loader but the first one I worked on was a 475 III A a little bigger than your 175. Actually had to rebuild the transmission in one of those down in Virginia, fun thing is you could completely strip the transmission without removing it from the machine!
Company I worked for had a 175, I believe I worked on absolutely every system but the brakes. Never even looked at them! I went to Tampa the week before Christmas and pulled the torque converter to bring home and rebuild, super rich retired Dr who owned the company laid everybody off on Christmas Eve, left the equipment inside Florida Steel.
I kind of knew Nige would like that(bladder brakes). But to be honest when working those 988A brakes would just about put you through the windshield! As would the parking brake once they went to the dry multidisc to replaced the Bendix drum brake!
We had those brakes on the front of early 773s as well. F’kin ***** they were......
Yea I believe I worked on a couple of those to. And id did include the disclaimer "when working" in my comment. Trying to remember where it was but recall seeing some military airplane on display and I swear it had brakes that sure looked like those off the 988A Cats. Might have been a 1940's to 1950's vintage bomber?